Immunization against bovine rotaviral infection.

Calves fed with colostrum from cows vaccinated with an inactivated rotavirus vaccine were refractory to experimental infection with strain 81/36F of bovine rotavirus. In the field study, 458 pregnant cows from 26 herds were involved. In each herd, cows were selected and randomly subdivided in two groups. Cows in one group (248 head in total) were vaccinated, whereas cows in the other group (210 head in total) were left as unvaccinated controls. At calving, colostrum was collected from each cow and stored at -30 degrees C until used for feeding calves. The newborn calves, beginning the second day of life and for the next 7-10 days, were each fed a daily supplement of 400 ml of colostrum from its dam. The diarrhea occurred in 86 (40.9%) calves that had received colostrum from unvaccinated dams (normal colostrum), and in 7 (2.8%) calves which were fed colostrum from vaccinated dams (immune colostrum). The disease was very severe in the normal colostrum-fed calves and 52 of them died. By contrast, the 7 immune colostrum-fed calves displayed a rather mild enteric condition, and all recovered without any sequela being observed.

Further studies on passive immunization of newborn calves against rotaviral infection.

An inactivated rotavirus vaccine was prepared with an adjuvant which gives a water-in-oil emulsion. The vaccine when injected into cows in their last month of pregnancy, proved to be as effective as the traditional vaccine, prepared with the Freud's incomplete adjuvant, in enhancing the lactogenic immunity. Thus, feeding experimentally infected calves with colostrum and first milk from vaccinated cows prevented diarrhea and reduced significantly rotavirus shedding. Because of its low grade viscosity the water-in-oil emulsifier facilitates inoculation of the vaccine and is therefore recommended as an adjuvant in the preparation of inactivated rotavirus vaccine.

The protection of newborn calves against experimental rotavirus infection by feeding mammary secretions from vaccinated cows.

Pregnant cows were given the first injection of an inactivated bovine rotavirus vaccine approximately 4 weeks before calving and a second injection just before calving. This led to the enhancement of rotavirus antibody titers in their colostrum as well as in the milk for at least 5 days after parturition. Thus, when newborn calves were fed with the mammary secretions obtained from the vaccinated cows daily for 5 consecutive days they were fully refractory to experimental infection with 81/36F bovine rotavirus. By contrast, the calves which were given the mammary secretions from unvaccinated cows, had clinical signs consistent with rotavirus infection and viral shedding. Based on these results it is suggested that vaccination of cows according to the scheme followed in this experiment, i.e., two injections within the last month of pregnancy, might be a valid approach which depending on confirmation under field conditions, could help reduce the incidence of rotavirus-induced diarrhea in newborn calves.

Neonatal calf diarrhea induced by rotavirus.

This presentation summarizes the results of a comprehensive study on rotaviruses isolated in Italy from calves and rabbits affected by neonatal diarrhea. The results clearly indicated that rotavirus infection is widespread and supported the evidence for an etiologic role of these viruses in neonatal diarrhea. The evidence of differences in virulence among bovine rotaviruses appeared also to be confirmed. Conventionally reared calves were fully susceptible to the experimental infection induced by three rotaviruses originating from heterologous hosts, i.e. monkeys, pigs and rabbits, respectively. When rotavirus strains of bovine, simian, porcine and rabbit origin were compared by cross neutralization tests, it was found the simian and porcine strains were indistinguishable and both appeared to relate antigenically to the bovine strain. On the other hand, a reciprocal antigenic correlation was found between bovine and rabbit isolates. Finally, it was proven that feeding newborn calves with colostrum of their dams, previously vaccinated with an inactivated rotavirus vaccine, could prevent the neonatal diarrhea from occurring.

Field trial evaluation of an inactivated rotavirus vaccine against neonatal diarrhea of calves.

Field trials were conducted using an inactivated rotavirus vaccine for prevention of calf neonatal diarrhea. For the trials, 458 pregnant cows from 26 herds were involved. In each herd, cows which had been inseminated within a period of two months were selected and randomly subdivided in two groups. Cows in one group (248 head in total) were vaccinated 6 weeks before calving and again 4 weeks later; cows in the other group (210 head in total) were left as unvaccinated controls. At calving, colostrum was collected from each cow and stored at -30 degrees C until used for feeding calves. The newborn calves, beginning the second day of life and for the next 7-10 consecutive days, each was fed a daily supplement of 400 ml of colostrum from its dam. The diarrhea occurred in 86 (40.9%) calves that had received colostrum from unvaccinated dams (normal colostrum), and in 7 (2.8%) calves which were fed colostrum from vaccinated dams (immune colostrum). The disease was very severe in the normal colostrum-fed calves and 52 of them died. Those calves which survived the disease underwent a significant loss of condition. By contrast, the 7 immune colostrum-fed calves displayed a rather mild enteric condition, and all recovered without any sequela being observed.

The efficacy of colostrum from cows vaccinated with rotavirus in protecting calves to experimentally induced rotavirus infection.

Calves which were continuously fed colostrum from vaccinated cows for the first ten days of life, were fully refractory to experimental infection with strain 81/36 F of bovine rotavirus. By contrast, the response to virus exposure of calves which were treated with normal colostrum was identical to that of the control calves, in that they underwent severe diarrhea and a significant slowing of the growth rate. The antibody titer in the milk of vaccinated cows tends to decline rapidly so that it no longer provides any protective effect. Two alternatives were considered feasible in improving prophylaxis for rotavirus infections: (a) the continuous feeding of calves with 1st day colostrum as part of the ration throughout the period of greatest risk (first week of life), or (b) enhancing the efficacy of the vaccine in pregnant cows to the point where antibody concentration in the milk would remain at a protective level.